SME
Inorganic Chemistry
Hard and soft acids and bases
Use this for “Is Ag⁺ a hard or a soft acid? Will it bind I⁻ or F⁻ more strongly?”
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Is the Lewis acid hard, borderline or soft?
Tap a card, then tap its group.
Look at the ion’s size and charge: small and highly charged is hard; large, low in charge and rich in d electrons is soft.
Assumptions
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A Lewis acid accepts an electron pair; here each acid is a metal ion or H⁺.
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Hard acids are small, highly charged and hard to polarize; soft acids are large, low in charge and easy to polarize.
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Hard acids bind hard bases best and soft acids soft bases (Pearson’s rule), so the class predicts which complexes are stable.
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